Extraction is an indispensable process step in the production of tea powders and ready-to-drink (RTD) beverages. In the prior art, many extraction technologies have been developed or proposed (e.g. microwave-assisted or ultrasound-assisted extraction, ultra-high-pressure extraction), but one type that is used widely in industry is a hot water extraction method based on a batch treatment method, e.g. in-tank extraction and metal grid extraction. In general, for the production of a 1× concentrated liquid which can be used directly to manufacture an RTD beverage product, one or two batches may be sufficient in a hot water extraction method using batch treatment, e.g. primary liquid production. In order to prevent undesired components (mainly having bitter and astringent tastes) from entering the final extract, the use of a short extraction time (10 to 30 minutes) and a relatively low temperature (representatively 50° C.-80° C.) becomes a necessary condition. Furthermore, to maintain a high extraction yield, the ratio of water to starting material must be high (e.g. 50:1). In general, the batch treatment method is indeed a simple, quick and low-cost extraction process method. However, these advantages of the batch treatment method are at the expense of aroma, concentration and extraction efficiency. The strength of aroma in a tealeaf liquid prepared by the method is low, not only because of the loss due to volatilization that is widely believed to occur during extraction, but also because of a low extraction yield caused by low temperature and short contact time, as well as the use of polar solvents for non-polar aromatic components in tealeaves. Clearly, a significant amount of aromatic substances are retained in the starting material after batch extraction.
Thus, a need has developed for a technique capable of imparting desired sensory properties to tea concentrate. Although a 1× concentrated liquid (<1 degree Brix) obtained by a conventional extraction method (such as the batch extraction method) is sufficient in the case of the production of primary liquid or similar products, a high concentration step is inevitable in the case of the production of concentrates. In the prior art, a large amount of water must be removed in the concentration step, and this will not only consume a large amount of energy, but also lead to huge wastage of aromatic substances and a change in the sensory properties of the final product. Moreover, when the batch extraction method is used, it is also very difficult to prevent undesired attributes in the starting material (e.g. bitter and astringent taste attributes) from entering tea solution from leachate.
Another method of producing tea extract is column extraction. A column body is packed with tealeaves, and hot water enters via the column bottom and passes through the entire column. A concentrated tealeaf extract exits through a top end of the column, and is rapidly cooled to room temperature or below. An advantage of the method is that a tealeaf concentrate (e.g. 5-20 degrees Brix) can be produced without an additional concentration step, so that aromatic substances in tealeaves are retained very well in the production process.
Although documents in China and abroad have disclosed the manufacture of a liquid tea extract using a column extraction method with water as a solvent, the method used therein to treat the liquid extract is direct discharge thereof, and the objective thereof is to make the extraction efficiency of at least one substance in the liquid extract higher. In the present invention, on the other hand, eluent is collected in sections continuously according to the elution volume, to achieve separation of tastes, and collected liquid extracts of different sections can also be recombined to obtain products of different tastes according to the taste variation shown in a relative taste intensity curve.